Many medical adhesives are known. Often, these adhesives are copolymers of hydrophobic water-insoluble monomers such as isooctyl acrylate and a small amount of a water-soluble monomer such as a short chain .alpha.,.beta.-unsaturated carboxylic acid or an N-vinyl lactam. While these copolymers make excellent medical adhesives, the presence of substantial amounts of ionic or highly polar solvents results in phase separation.
Conductive adhesives have been known for many years. One class of conductive adhesives has employed homopolymers or copolymers of N-vinyl lactams such as N-vinyl-2-pyrrolidone. U.S. Pat. Nos. 4,273,135 and 4,352,359 (both Larimore et al.) disclose non-ionic water-soluble polymers prepared from N-vinyl lactams. However, no crosslinking of such polymers is disclosed. Crosslinking allows for higher amounts of a plasticizer for the composition without reducing cohesiveness of the composition below acceptable levels.
U.S. Pat. Nos. 4,527,087 and 4,539,996 (both Engel) disclose the polymerization of an unsaturated free-radically polymerizable material which is soluble in a polyhydric alcohol, where the unsaturated material is crosslinked with a multifunctional unsaturated free-radically polymerizable material. U.S. Pat. No. 4,554,924 (Engel) discloses a conductive adhesive formed by an essentially solventless free-radical polymerization of an adhesive precursor having a polyhydric alcohol, at least one non-ionic monomer, an initiator, a crosslinker, and an ionizable salt present in amounts sufficient to render the composition electrically conductive. One of the non-ionic free-radically polymerizable monomers can be N-vinyl pyrrolidone. The essentially solventless precursor can be coated onto the electrode plate or transfer sheet and exposed to either heat or actinic radiation which forms the electrically conductive pressure-sensitive adhesive. The precursor may also be exposed to electron beam radiation to facilitate the crosslinking.
U.S. Pat. No. 4,848,353 (Engel) discloses an electrically-conductive, pressure-sensitive adhesive composition of a homogeneous mixture of a copolymer matrix and a plasticizing, electrically-conductive solution. The composition need not be covalently crosslinked but a crosslinker may be used. The copolymer matrix is formed from a free-radical polymerizable adhesive precursor having at least one water-soluble hydrogen bond donating monomer, at least one water-soluble hydrogen bond accepting monomer, and either a photo or thermal free radical initiator. N-vinyl lactams may be used as the hydrogen bond accepting monomer with N-vinyl pyrrolidone being preferred.
European Pat. Publication 0322098 (Duan) discloses a crosslinked hydrophilic polymer composition which is useful as a pressure-sensitive adhesive. The composition comprises a crosslinked, cohesive, swellable polymeric matrix and a plasticizing solution. The crosslinked, cohesive, swellable polymeric matrix is formed from the free-radical polymerization of a precursor having a monomeric species of N-vinyl lactam, and a crosslinker of a multi-ethylenically unsaturated compound wherein the ethylenic groups are vinyl, allyl, or methallyl groups bonded to nitrogen or oxygen atoms. The crosslinker and plasticizer are present in controlled amounts sufficient to render a pressure-sensitive adhesive swellable matrix.
A continuing concern for the preparation of hydrophilic polymers used as medical adhesives is biocompatibility. Not only must the pressure-sensitive adhesive composition adhere to mammalian skin, but also the adherence to mammalian skin must not cause skin irritation, toxicity reaction, or other deleterious effects of contacting a polymeric composition to living tissue. Compositions which are prepared by the polymerization of monomers must proceed through exacting procedures to minimize the residual presence of unreacted monomers. When crosslinking agents are employed to chemically crosslink a polymer, such crosslinking agents can also leave residuals and produce undesired byproducts.
Another approach to preparing conductive adhesives involves irradiation crosslinking of uncrosslinked polymers in the presence of plasticizers. U.S. Pat. Nos. 4,699,146 and 4,750,482 (Sieverding) disclose a water-insoluble, hydrophilic elastomeric, pressure-sensitive adhesive that includes at least one irradiation crosslinked synthetic organic polymer and an adhesive plasticizer. The crosslinked polymer is formed by dispersing or solubilizing at least one suitable gel-forming, uncrosslinked synthetic organic polymer in a plasticizer that has a composition the same as or different than the adhesive plasticizer, and then subjecting the resulting solution or dispersion to an appropriate dosage of irradiation. One example of an uncrosslinked synthetic organic polymer includes repeating units derived from an N-vinyl lactam monomer which is preferred among monomeric candidates. The solubilizing plasticizer includes at least one substantially non-volatile elasticizer and conveniently includes a volatile solvent which can be aqueous, nonaqueous, or a mixture. Preferably the volatile solvent is water. The substantially non-volatile elasticizer can be a polyhydric alcohol, a lactam, a glycol, among others listed. But it is necessary that the elasticizer present during the irradiation treatment step be irradiation crosslinking compatible. Glycerin tends to reduce effectiveness of irradiation crosslinking and should not be present prior to irradiation treatment in an amount greater than about 5% of the total formula weight. Glycerin can be added once crosslinking has been completed.
However, ionizing radiation of a plasticizing liquid can produce small molecule contaminants and other byproducts when ionizing crosslinking is performed on polymers in the presence of other materials. Further, adhesive gels containing levels of plasticizing glycerin greater than about 5% of the total formula weight cannot be directly prepared since glycerin containing precursor solutions do not crosslink upon exposure to ionizing radiation. Thus, these Sieverding patents teach a cumbersome process of plasticizing an ionizing radiation crosslinked polymer.
Other U.S. patents have also disclosed the irradiation of poly(N-vinyl lactam) in the presence of other materials. U.S. Pat. No. 4,089,832 (Yamauchi et al.) discloses the crosslinking of polyvinyl pyrrolidone while in aqueous solution followed by pulverizing the crosslinked product and mixing with a plastic substance selected from thermoplastic or thermohardenable plastics.
U.S. Pat. No. 3,900,378 (Yen et al.) discloses a particulate polymer useful as a soil amendment prepared by blending a mixture of a hydrophilic polymer, a pulverulent inert filler, and water prior to exposing the mixture to ionizing radiation for a period of time to crosslink the polymer.
U.S. Pat. No. 4,646,730 (Schonfeld et al.) discloses an aqueous dispersion of polyvinyl pyrrolidone, silver sulfadiazine, magnesium trisilicate and water, followed by exposure to E-Beam radiation to provide a hydrogel product having a uniform deep yellow color retained over a long shelf life.
U.S. Pat. No. 4,989,607 (Keusch et al.) discloses hydrophilic gels which are nonstringy and highly conductive, prepared from an aqueous mixture of poly(vinylpyrrolidone) a viscosity-enhancing hydrophilic polymer, and an electrolyte to provide a uniform cohesive aqueous mixture substantially free of unbound water. The aqueous mixture is applied or cast to a desired thickness and subjected to crosslinking high energy irradiation to initiate or precipitate the crosslinking polymer chains.
European Pat. Publication 0 107 376 (Thompson et al.) discloses a gel dressing made from poly(vinylpyrrolidone) having a high molecular weight by dissolving the polymer in water and crosslinking the polymer with ionizing radiation for time sufficient to change the viscosity of the solution.
U.S. Pat. No. 4,792,400 (Dougherty et al.) discloses preparation of a particulate, normally solid, water-insoluble vinyl lactam polymer containing between about 0.5 and about 10% of non-crosslinked and/or unsaturated sites on the high molecular weight polymer chains. These polymers have an average particle size sufficient to be retained on a filtering means. The water-insoluble polymer is subjected to irradiation with radiant energy at a dosage level of between about 0.001 and about 20 megarads. The polymeric materials can be irradiated in a dry state or as a liquid slurry.
U.S. Pat. No. 4,904,247 (Therriault et al.) discloses a pressure-sensitive hydrophilic laminate composite comprising layers of a tacky pressure-sensitive adhesive hydrophilic polymer blend and a non-tacky hydrophilic polymer blend. The blends are preferably comprised of homopolymers or copolymers of N-vinyl lactam, a relatively hydrophobic water-insoluble acrylate polymer and water soluble plasticizer. The blends have a microphase separated morphology. Pressure-sensitive adhesiveness is determined by the amount of N-vinyl lactam polymer and the amount of plasticizer in the blend.